(1) Field of the Invention
The present invention relates to a device for regulating the speed of rotation of at least one main rotor of a rotorcraft, known as the speed NR. Such a speed NR is thus a function directly of the quantity of fuel injected into the engine for producing combustion that is to drive rotation of the main rotor.
Thus, the present invention also lies in the field of methods of regulating the operation of one or more engines in a power plant of a rotorcraft. By way of example, such a power plant may have at least one main fuel-burning engine, in particular a turboshaft engine, conventionally delivering the mechanical power needed by the rotorcraft for driving at least one or more rotors of the rotorcraft.
Consequently, the present invention lies more specifically in the context of a device and a method for driving at least a main rotor of the rotorcraft, and possibly also for driving an anti-torque rotor, if any, at a setpoint speed that is variable.
(2) Description of Related Art
The main rotor typically provides the rotorcraft at least with lift and possibly also with propulsion and/or changes of attitude in flight for the specific circumstance of a helicopter. The anti-torque rotor typically provides stabilization for the rotorcraft and guidance in yaw, and it is commonly in the form of a tail rotor or at least one propulsive propeller for a rotorcraft having a high speed of advance.
Conventionally, the operation of the main engines of a rotorcraft is under the control of a regulator unit, such as a full authority digital engine control (FADEC). The regulator unit controls the metering of fuel to the main engines as a function of a setpoint, referred to below as the NR setpoint, relating to a speed of rotation that is required from the main rotor. The NR setpoint may thus be generated by the regulator unit (FADEC) under certain particular circumstances. In other particular circumstances, e.g. when the NR setpoint is variable, the NR setpoint may be generated by the electronic, electrical, and computer equipment of the rotorcraft as a whole and then transmitted to the regulator unit (FADEC) by management means, such as an automatic flight control system (AFCS). Under such circumstances, the regulator unit (FADEC) serves to regulate the speed NR.
Thus, the NR setpoint may be transmitted by the management means (AFCS) as a function of the requirements of the rotorcraft for mechanical power as identified depending on the current flight circumstances of the rotorcraft, and in particular as a function of mechanical power requirements for driving the main rotor. By way of example, the power consumed by the main rotor may be identified by evaluating firstly the resisting torque that the main rotor opposes against being driven by the power plant, and secondly by its speed of rotation.
Nevertheless, technical progress in the field of rotorcraft is tending towards driving the main rotor at a controlled speed NR that is variable relative to the nominal speed NR1 as predefined for the most critical conditions for the rotorcraft, e.g. corresponding to occasional complex procedures for takeoff or landing, commonly referred to by the term “CAT A procedures”.
Specifically, such significant variation in the speed NR at which the main rotor is driven can be used for optimizing the level of power delivered by the engine as a function of the associated stage of flight, e.g. in order to reduce noise nuisance close to the ground and/or in order to improve performance. By way of indication, the speed of the main rotor may be controlled to vary over a range within 5% to 10% of the nominal speed NR1, and potentially over a larger range depending on technical progress, and more particularly it may be controlled to vary over a range of values that might lie from 90% to 115% of the nominal speed NR1.
On this topic, reference may be made for example to the publication “Enhanced energy maneuverability for attack helicopters using continuous variable rotor speed control” (C. G. Schaefer Jr., F. H. Lutze Jr., 47th Forum American Helicopter Society 1991, pp. 1293-1303). According to that document, the performance of a rotorcraft in a combat situation is improved by varying the speed at which the main rotor is driven, depending on variation in the air speed of the rotorcraft.
Reference may also be made for example to Document U.S. Pat. No. 6,198,991 (Yamakawa et al.), which proposes reducing sound nuisance generated by a rotorcraft approaching a landing point by varying the speed of rotation of the main rotor.
Reference may also be made on this topic by way of example to the Document US 2007/118254 (G. W. Barnes et al.), which proposes varying the speed of rotation of the main rotor of a rotorcraft using two values referred to as high and low, under predefined threshold conditions for values of various parameters associated with previously-identified flight conditions of the rotorcraft.
Also by way of example, reference may be made on this topic to the Document WO 2010/143051 (Agusta Spa et al.), which proposes varying the speed of rotation of a main rotor of a rotorcraft in compliance with a map that has previously been drawn up depending on various flight conditions of the rotorcraft.
Finally, as described by the Applicant in Document FR 3 000 466, it is also known to use an altimeter in order to act automatically to control variation in the speed of rotation over a range from 90% to 110% of a predetermined nominal value.
Furthermore, Documents FR 2 974 564, GB 2 192 163, and FR 2 981 045 describe other devices or methods for regulating a main rotor or a tail rotor of a rotorcraft.
Nevertheless, although such documents describe devices or methods for regulating the speed NR during the flight of a rotorcraft, none of those documents provides a solution enabling the speed NR to be regulated automatically while a rotorcraft is taxiing on the ground, and more particularly during the stages that precede takeoff or that follow landing of such a rotorcraft.